Electron discharge device circuits



May 23, 1944.. J, E YOUNG 2,349,534 I ELECTRON DISCHARGE DEVICE CIRCUIT Filed Dec'. so, 1941 mfg/vwl j @Wi rmentor Gttorneg Patented May 23, 1944 UNITED S'I'A'If-ES4 PATNT ost-'ics 2,349,534 ELECTRON DISCHARGE DEVICE CIRCUITS John a Young, osklyn, N. A.1., signor ai Radio Corporation o! America, a.corporation of Delaware Application December 30, 12941, Serial No. 424,878

3 Claims.

This invention relates to improvements in electron discharge device circuits. Although the invention is hereinafter described with particular reference to a transmitter it should be understood that the novel features thereof are not lim-` ited to transmitting equipment, and have application to receivers as well as to industrial equipment which may have no relation to communica-- tion systems.

One feature vof the present invention comprises a push-pull electron 4discharge device system hav-y ing a pair ofY vacuum tubes whose grids are sup-f plied .with bias through individual resistors.

,Broadly, this feature applies to any arrangement of vacuum tubes which contribute their output energies to a common utilization circuit, or, putting it another way, the feature is applicable to vacuum tubes whose inputs are connected in parallel as well as to vacuum tubes whose inputs are connected in push-pull.

Another feature ofthe present invention comprises the use of a high readtance transformer in vthe filament circuit of a vacuum tube for the purpose of limiting the starting current.

Still 'another feature resides in the use of one or more voltage limiter tubesof the gaseous type across the primary winding of aftransformerl for protecting a vacuumtube from surges of power `a metallic surface spaced from the elongated anode to form a capacity therewith, which surface is movable in a direction over the length-of the anode socket tovary the capacity therebetween.

A more detailed description of the invention follows in conjunction with the drawing, wherein:

Fig. 1 illustrates, by way of example only, a' frequency modulation transmitter embodying the Y features of the invention; and

Fig. 2 illustrates the novel tuning means of the invention which can be used as an alternative for the plate-tank tuning circuit of Fig. l.

Referring to Fig. 1 .in more detail, there is shown a frequency modulation transmitter com prising a pair of pushlpull connected power ampliiier vacuum tubes I and 2, each of which has which may, if desired, be adj an.anode, a cathode and a grid. The grids are shown connected together through a tuned inputv circuit 3 comprising leads I and-5 and by/-pass condenser 6. A pairof series arnanged venier 5 tuning condensers 1, l are connected across the conductors 4 and 5 at a Jsuitable location spaced from theby-pass condenser 6. The grids of the vacuum tubes I and Z are individually supplied with suitable bias potentials thr ugh resistors B, 8

table to compensate for any difference in the characteristics of the vacuum tubes. vIn practice, it is preferred that the vacuum tubes I and 2 be identical in type, in which case resistors 8, 8 will be o'f the same value. By supplying the grids with individual biases as shown, the effect of-a slight diierence in the dynamic characteristics of the vacuum tube is prevented from seriously affecting lthe 4opera-- ton of the tubes. The frequency modulated in- Dut waves are applied to the tuned input circuit 3 by means of line 9 whose conductors are slidably connected to the leads 4- and 5. It should be noted thatconnection of the circuit 9 to the input tuned'cirpuit occurs.at points beween the condensers 5 and 1, 1.

The filaments of the vacuum tubes areA shown connected together and to ground, from a radio frequency standpoint, by means of condensers IIL. and are individually supplied with heating energy from a two-phase supply through high reactance type transformers l I, I I. Although the filaments are shown connected to individual transformers, it should be` understood from a practical standpoint that, if desired, these filaments maybe as connected together to thesecondary winding of a single high reactance type transformer. The f use of a two-phase supply with individual transformers for the different filaments has the ad- Y vantage of minimizing the eifect of the lament tion of the output of the transmitter. The purpose of the high reactance transformer II is to limit the surge of current through the filament when the filaments are first energized. The

transformers are so designed that they have suiiicient reactance'toprevent the initial in-rush current from exceeding twice the normal running current of the lament, thereby assuring Afreedom from mechanical strains or breakage in the filament structure. These high reactance transformel-s comprise, in effect, a pair of loosely couv pled windings so designed that a certain amount lof leakage between the windings is deliberately introduced. Erom a practical standpoint, the primary and secondary windings oi' each trans- 4o heating current introducing amplitude modula`A former,I I can have a common core with windings either coiled around different portions of the core, or else coiled around the same portion of the core but suitably spaced to give the desired result.

The anodes of the pushpull lpower amplifier tubes I, 2 are connected together through a tuned circuit I2 whose tuning can be varied by means of a slider I3 bridged across the conductors of the tuned circuit. Output energy which may be /supplied to a vsuitable antenna, not shown, is

derived from the pick-up loop I 4 located in the field of the tuned circuit I2. This pick-up loop is U-shaped in form and has one leg thereof coupled to one conductorlof the output tuned circuitI and the other leg thereof coupled to the other conductor of the output tuned circuit. One terminal of the loop is connected to ground through condenser I6. By varying the angularv position of the loop, there is obtained a variation` in the magnitude of the output induced in the loop from the tank circuit I2. A positive polarizing potential is supplied to the anodes by means lof lead I1 which is connected in series with a choke and ,resistor parallel combination I9. The choke coil serves to block radio frequency energy from the power supply while the resistor serves to parasitic oscillations.

A portion of theoutput energy is taken olf through condenser 20 and rectified in 2l, then amplified in 22 to feedback to the plate tuned damp circuit I2 through transformer I8 energy to reduce the magnitude of the amplitude modulation noise. In effect, the circuit 20, 2I, 22 and I8 may be considered a feed back lamplifier which picks up a portion of the carrier output of the transmitter, recties. it, and then amplies the resulting amplitude modulation signal caused by hum and noise, to thereby modulate the power amplifier stage. The phase relations and gain of this feed back amplifier are such that :amplitude modulated noise ofthe transmitter is reduced by a considerable amount. The feed back amplifier serves not only to reduce the noise but 'also to reduce the undesired amplitude modulations vpresent as a result of the signal. Tio protect the vacuum tubes in apparatus .22 from surges in the power amplifier, due to some failure in either vacuum tubes I and 2 or the circuits associated with these tubes causing a current in the 4secondary winding of transformer I8 to induce a high voltage in the primary winding of this transformer, there are provided a pair of gaseous voltage llimiter tubes 23, 23 arranged in series relation and across the primary winding of transformer I8, as shown. Although two voltage limiters are shown in series, it should be understood that, if desired, they may 'be replaced by a single voltage limiter tube of .the proper rating.

In one embodiment of the systemof Fig. 1 constructed and successfully reduced tolpractice', the

system functioned to amplify a frequency modu' lated input in the range of from 42 to 50 megacycles. The 'vacuum tubes l and 2 were RCA 889B type tubes, the resistors 8, 8 were each composed of two resistors in series of 1600 ohms each, the condenser 6 had a value of approximately 200 mmf., theamplifier 2I was an RCA 6ZY5G. while the amplifier 22 consisted of three stages `comprising a first audio stage havingan RCA 6J7 tube, the second audio stage comprising an RCA 807 tube, and a modulator stage comprising '2 four RCA 845 tubes in parallel.

1 a'variable condenser I5, while the other terminal yis connected to the load circuit through a variable Fig. 2 shows an alternative form of tuning arrangement for the plate-tank circuit I2 which can be used instead of the bridging-slider I3 of Fig. 1. The tuning system of Fig. 2 is applicable primarily to vacuum tubes having an elongated metallic anode or metallic anode circuit which is usually the casein high power amplifiers where fluid cooling of the anode is employed. The

power ampliers I and 2 are shown in Fig. A2

diagrammatically only, the elongated anodes A, A being designated since these are the only elements of the tubesnecessary for an understand# ing`of the novel tuning feature to be described. The elements A, A may either be the elongated anodes or metallic shells-into which the anodes are inserted and directly connected. These shells may serve for mounting the vacuum tubes. Variation in tuning is obtained by means of sliding metallic block 24 shaped inv the -form of a triangle to fit in the space between the two jackets A, A so as to be movable vertically'up or down in the space between them. The metallic block has arcuate shaped grooves adjacent both jackets A, A of the. vacuum tubes I and 2 and is capacitively coupled thereto. This block is movable in a vertical direction by means of a threaded guide or lead screw 25 in turn linked to a suitable dial or handle 26. It will be apparent that as themetallic surface 24 is moved in adownward direction, that less and less of the surface of the block becomes adjacent to the anode shells A, A, asa consequence of which there will be less and less capacity between the anodes. By the same token, as the metallic surface 24 moves upward, more and more of its surface will become adjacent the anode shells A, A, as a result of which y therewill be more and more capacity between the anodes of the device. This movement of the block 2B, with its consequent change in capacity between the anodes, cause a change in the capacity andmhence a change in the tuning of theoutput tank circuit I2. In the particular vacuum tubes I and 2 used in 'the construction successfully tried out in practice and referred to above,

o the anodes had metallic fins connected to them to aid in heat radiation, and these ns were inserted into the anode sockets A, A vwhich consisted' merely of a metallic sheet surrounding the edges of the fins and directly joined thereto.

What is claimed is:

1. In combination, a pair of electron discharge devices having their anodes mounted in vertically arranged cylindrical metallic sockets, a tuned circuit connected to said anodes, a tuning element capacitively coupled to both sockets, and

` control means for moving said tuning element vertically to bring more or less` surface adjacent said sockets, said tuning element having arcuate grooves adjacent and enclosing at least a portion of said cylindrical metallic sockets, said control means comprising a lead screw threadedly engaging said tuning element.

2. In combination, a pair of electron discharge devices having their anodes mounted in vertically arranged cylindrical metallic sockets, a tuned circuit connected to said anodes, and an elongated metallic tuning element capacitively coupled to both sockets, said tuning element having arcuate grooves adjacent and enclosing at least a portion of said cylindrical metallic sockets and which grooves terminate in a vertical line midway between said sockets,\and means for moving said Atuning element-vertically to bring mor(` or'less of its surface adjacent said sockets.

3. In combination, a pair of electron discharge devices having their anodes mounted in paralleliy Aarranged cylindrical metallic sockets, a. tuned circuit connected to said anodes, and an elongated metallic tuning element capacltively coupled to both sockets, said tuning element having arcuate grooves adjacent and enclosing at least face adjacent said sockets.

JOHN E. YOUNG. 

